This invention relates in general to a vehicular drive train assembly including a transmission and a multiple speed axle for providing a desired speed reduction gear ratio between a source of rotational power and the driven wheels of the vehicle. More particularly, this invention relates to an integrated system for automatically controlling the operation of both an automated mechanical transmission and a multiple speed axle assembly in such a vehicle drive train assembly.
In virtually all land vehicles in use today, a transmission is provided in a drive train assembly between a source of rotational power, such as an internal combustion or diesel engine, and the driven axle and wheels of the vehicle. A typical transmission includes a case containing a transmission input shaft, a transmission output shaft, and a plurality of meshing gears. Means are provided for connecting selected ones of the meshing gears between the transmission input shaft and the transmission output shaft to provide a desired speed reduction gear ratio therebetween. The meshing gears contained within the transmission case are of varying size so as to provide a plurality of such gear ratios. By appropriately shifting among these various gear ratios, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.
To facilitate the operation of the transmission, it is well known to provide a clutch between the vehicle engine and the transmission. When the clutch is engaged, the transmission is driven by the vehicle engine to operate the vehicle at the selected gear ratio. To shift the transmission from a first gear ratio to a second gear ratio, the clutch is initially disengaged such that power is not transmitted from the vehicle engine to the transmission. This allows the gear shifting operation to occur within the transmission under a non-torque loading condition to prevent undesirable clashing of the meshing gear teeth. Thereafter, the clutch is re-engaged such that power is transmitted from the vehicle engine to the transmission to operate the vehicle at the second gear ratio.
A typical structure for a vehicle clutch includes a cover that is connected to a flywheel secured to the end of the output shaft of the vehicle engine for rotation therewith. A pressure plate is disposed within the clutch between the cover and the flywheel. The pressure plate is connected for rotation with the flywheel and the cover, but is permitted to move axially relative thereto. Thus, the flywheel, the cover, and the pressure plate are all constantly rotatably driven by the vehicle engine. Between the flywheel and the pressure plate, a driven disc assembly is disposed. The driven disc assembly is supported on the transmission input shaft for rotation therewith, but is permitted to move axially relative thereto. To engage the clutch, the pressure plate is moved axially toward the flywheel to an engaged position, wherein the driven disc assembly is frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the transmission input shaft upon which it is supported) are driven to rotate with the flywheel, the cover, and the pressure plate. To disengage the clutch, the pressure plate is moved axially away from the flywheel to a disengaged position. When the pressure plate is moved axially to this disengaged position, the driven disc assembly is not frictionally engaged between the flywheel and the pressure plate. As a result, the driven disc assembly (and the transmission input shaft upon which it is supported) are not driven to rotate with the flywheel, the cover, and the pressure plate.
To effect such axial movement of the pressure plate between the engaged and disengaged positions, most vehicle clutches are provided with a release assembly including a generally hollow cylindrical release sleeve which is disposed about the transmission input shaft. The forward end of the release sleeve extends within the clutch and is connected through a plurality of levers or other mechanical mechanism to the pressure plate. In this manner, axial movement of the release sleeve causes corresponding axial movement of the pressure plate between the engaged and disengaged positions. Usually, one or more engagement springs are provided within the clutch to urge the pressure plate toward the engaged position. The engagement springs typically react between the release sleeve and the cover to normally maintain the clutch in the engaged condition. The rearward end of the release sleeve extends outwardly from the clutch through a central opening formed through the cover. Because the release sleeve is connected to the cover and the pressure plate of the clutch, it is also constantly driven to rotate whenever the vehicle engine is operating.
Thus, an annular release bearing is usually mounted on the rearward end of the release sleeve. The release bearing is axially fixed on the release sleeve and includes an inner race which rotates with release sleeve, an outer race which is restrained from rotation, and a plurality of bearings disposed between the inner race and the outer race to accommodate such relative rotation. The non-rotating outer race of the release bearing is typically engaged by an actuating mechanism for moving the release sleeve (and, therefore, the pressure plate) between the engaged and disengaged positions to operate the clutch.
In a conventional mechanical transmission, both the operation of the clutch and the gear shifting operation in the transmission are performed manually by an operator of the vehicle. For example, the clutch can be disengaged by depressing a clutch pedal located in the driver compartment of the vehicle. The clutch pedal is connected through a mechanical linkage to the outer race of the release bearing of the clutch such that when the clutch pedal is depressed, the pressure plate of the clutch is moved from the engaged position to the disengaged position. When the clutch pedal is released, the engagement springs provided within the clutch return the pressure plate from the disengaged position to the engaged position. Similarly, the gear shifting operation in the transmission can be performed when the clutch is disengaged by manually moving a shift lever which extends from the transmission into the driver compartment of the vehicle. Manually operated clutch/transmission assemblies of this general type are well known in the art and are relatively simple, inexpensive, and lightweight in structure and operation. Because of this, the majority of medium and heavy duty truck clutch/transmission assemblies in common use today are manually operated.
More recently, however, in order to improve the convenience of use of manually operated clutch/transmission assemblies, various structures have been proposed for partially or fully automating the shifting of an otherwise manually operated transmission. In a partially or fully automated manual transmission, the driver-manipulated clutch pedal may be replaced by an automatic clutch actuator, such as a hydraulic or pneumatic actuator. The operation of the automatic clutch actuator can be controlled by an electronic controller or other control mechanism to selectively engage and disengage the clutch without manual effort by the driver. Similarly, the driver-manipulated shift lever may also be replaced by an automatic transmission actuator, such as a hydraulic or pneumatic actuator which is controlled by an electronic controller or other control mechanism to select and engage desired gear ratios for use.
In addition to the clutch/transmission structures described above, most land vehicles further include an axle assembly for transmitting the rotational power from the transmission output shaft to the driven wheels of the vehicle. A typical axle assembly includes a housing containing an axle input shaft that is connected through a differential gear assembly to a pair of axle output shafts. The axle input shaft is connected by a driveshaft assembly to the transmission output shaft so as to be rotatably driven thereby. The differential gear assembly splits the rotational power from the axle input shaft to the two axle output shafts and, therefore, rotatably drives the wheels of the vehicle. In some instances, the axle assembly is structured to provide only a single speed reduction gear ratio between the axle input shaft to the axle output shafts. In other instances, however, the axle assembly is structured to provide two (or possibly more) speed reduction gear ratios between the axle input shaft to the axle output shafts. Multiple speed axle assemblies are desirable because they extend the number of speed reduction gear ratios beyond those provided by the transmission in a relatively simple and cost efficient manner. For example, a four-speed transmission that is operaated in conjunction with a two-speed axle assembly provides a total of eight available gear ratios.
In these multiple speed axle assemblies, a manually operable mechanism is provided for shifting among the axle gear ratios. In the past, this manually operable mechanism included a mechanical linkage extending from the driver compartment of the vehicle to the axle assembly. The driver of the vehicle physically moved the mechanical linkage to shift among the axle gear ratios. More recently, however, this manually operable mechanism included an electrical switch connected to operate an electric motor provided on the axle assembly. The driver of the vehicle manually operated the electrical switch to control the operation of the electric motor to shift among the axle gear ratios.
As mentioned above, it is known to partially or fully automate the shifting of an otherwise manually operated transmission. However, a partially or fully automated transmission cannot readily be used with a manually operable multiple speed axle assembly. As mentioned above, the use of a multiple speed axle assembly is desirable because it extends the number of speed reduction gear ratios beyond those provided by the transmission in a relatively simple and cost efficient manner. Thus, it would be desirable to provide an integrated system for automatically controlling the operation of both an automated mechanical transmission and a multiple speed axle assembly in a vehicle drive train assembly.